The present invention relates to a method for monitoring the operational state of a capacitive sensor. It can be applied particularly usefully, but not exclusively, in measuring the passes of blades in a rotating machine or a turbomachine such as a turboreactor or an airplane turboprop engine, or an electric generator turbine for example. The invention is broader in scope since it can also apply to any system using a capacitive sensor under very difficult environmental conditions.
During the operation of the turbomachine, it is known to mount a capacitive sensor on the housing. Document US2010268509 describes an electrode constituted by the rotor and a counterelectrode constituted by the housing, in particular the inner layer of the housing particularly constituted by multiple sheets.
In general, it is possible to measure the passes of the blades in a rotating machine or a turbomachine in real time in a non-intrusive manner in order to extract therefrom the clearance between the housing and the tip of the blade as well as the vibrations of the blade. These two items of information, the clearance and the vibrations, are key items of information on the state of health of the blade, i.e. its mechanical integrity. They can be monitored in real time throughout the entire operational period of the machine, in particular via blade health monitoring (BHM).
It is known that capacitive measurements under these conditions are substantially affected by electrical line losses, due to electrical impedance of the transmission line.
Document JP2006170797 is known as describing a principle for compensating the parasitic elements of the transmission line.
Document FR2784179 describes a system for compensating the leakage currents from the transmission line by producing feedback loops from signals representative of the capacitance and conductance compensation.
However, like its environment, motor housing, blade, path, the non-intrusive sensor used to measure the clearance and the vibrations evolves over time as a function of the thermal and mechanical loads which are applied to it during operation.